(b) Draw a genetic linkage map showing map distances between met, thi, and pur.

Transcription

1 Botany 132 Final exam 2002 Name Please show all of your work in answering the questions below. 1. F- bacterial cells of genotype met - thi - pur - were conjugated with F+ cells with the genotype met + thi + pur +. After the conjugation reaction was interrupted, cells containing met + were selected and tested for the unselected markers thi and pur. The number of met + colonies with the following genotypes determned: thi + pur thi + pur - 0 thi - pur + 8 thi - pur - 52 (a) What is the gene order? The gene order is Met Pur - Thi (b) Draw a genetic linkage map showing map distances between met, thi, and pur. Met Pur: 52/460 x 100 = 11.3% recombination = 11.3 map units Pur Thi: 8/460 x 100 = 1.7% recombination = 1.7 map units Met11.3 mupur1.7 muthi 2. Three testcrosses with combinations of three linked genes were performed. The crosses and the inferred gametes produced by the tested parent were as follows: AB/ab X ab/ab: 40% AB, 40% ab, 10% Ab, 10% ab AD/ad X ad/ad: 46% AD, 46% ad, 4% Ad, 4% ad BD/bd x bd/bd: 44% BD, 44% bd, 6% bd, 6% Bd What is the probable genetic map of the three genes? Show your work. A- B: 20% recombination mu A-D: 8% recombination ADB B-D: 12% recombination 8 mu 12 mu

2 3. Crosses were made between two strains of yeast. Each strain of carried a different allele of the a gene. While most of the tetrads formed as a product of this cross were normal, one unusual tetrad was observed. Explain (using figures) how this tetrad could have been generated. Cross: a1 a3 + X a1 + a3 Abnormal tetrad: a1 + a3 a1 + a3 a1 + a3 + a1 a3 + Assume that a wild type allele for a1 (a1+) is A/T and the mutant allele is G/C. The abnormal tetrad has 3 copies of the wt allele and only one of the mutant allele this suggests that a heteroduplex was created during recombination and that the mutant allele was repaired to wild type. For example: for a1 at meiosis, there would be four chromatids: G G C C G G C A Recombination between one strand of chromatid 2 and 3 results in 2 hetero A C-- duplexes. If these are repaired, then T T the repair process can generate a wild A A allele (A/T0 or a mutant T T allele (G/c). In this case, both duplexes were repaired to generate the wt allele. 4. If a woman and a man are heterozygous for a gene, and if they have three children, what is the chance that all three will also be heterogygous? 0.5 x 0.5 x 0.5 = 0.125

3 5. In Drosophila, the three gene pairs for red eyes (cn + ) vs. cinnabar (cn), normal bristle number (rd + ) vs. reduced (rd), and long wings (vg + ) vs. vestigial (vg) are known to map to X chromosome. A female heterozygous for all three genes was crossed against a male fly with cinnabar eyes, reduced bristle number and vestigal wings. Map the position of these three genes to one another draw a map. Show your work. cinnabar, reduced, vestigial 406 cinnabar, reduced, long 46 cinnabar, normal vestigial 28 cinnabar, normal, long 3 red, normal, long 438 red, normal, vestigial 45 red, reduced, long 33 red, reduced vestigial 1 a) Calculate the map distances between the genes, and construct a linkage map of these loci. Show your work. Cn Vg: /1000 = x 100 = 9.5 mu Cn Rd: /1000 = x 100 = 6.5 mu Vg Rd: (1 + 3)/1000 = x 100 = 16 mu Vg mu Cn mu Rd mu b) Determine the coefficient of coincidence for this set of loci. COC = obs. # of DCO/exp.# of DCO = 4/0.095 (0.065) (1000) = 0.65

4 6. Draw the banding pattern you would expect to see on a DNA-sequencing gel if you annealed the primer 5 -CTAGG-3 to the following single-stranded DNA fragment and carried out a dideoxy sequencing reaction. 3 -G-A-T-C-C-A-A-G-T-C-T-A-C-G-T-A-T-A-G-G-C-C-5 A G T C 7. Use the supplied figure of the genetic code to complete the following table. Assume that reading is from left to right and that the columns represent transcriptional and translational allignments. T A C A C C A T G A C G DNA A T G T G G T A C T G C double helix A U G U G G U A C U G C mrna U A C A C C A U G A C G trna Met Trp Tyr Cys amino acids

5 8. Consider the inducible regulation of the lac operon. For both for β-galactosidase (z) and permease (y), is enzyme production by each of the following genotypes constitutive, uninducible or inducible? β-galactosidase permease a) I + p + o c z + y + constitutive constitutive b) I + p + o + z - y - / i - p + o c z - y + uninducible constitutive c) I + p + o + z + y - / i - p + o c z - y + inducible constitutive d) I + p + o c z + y - / i s p + o + z - y + constitutive uninducible e) i s p + o + z + y - / I + p + o + z - y + uninducible uninducible 9. The molecule 2-aminopurine is an analog of adenine that pairs with thymine. It also occasionally pairs with cytosine. What types of mutations will be induced by 2- aminopurine after two rounds of replication? (Show your reasoning) A AP AP AP G T T C C or T C----- Results in an A/T - > G/C transition

6 A set of seven different rii deletion mutants of bacteriophage T4, 1-7, were mapped, with the following result: (the lines indicate the extent of the deletion) 1(b)(e) (a)(c)(d) Five rii point mutants were crossed with each of the deletions, with the following results, ( + = r + recombinants and 0 = no r + recombinants) Point Deletion Mutants Mutants a b c d e Map the locations of the point mutations.

7 10. In the Meselson and Stahl experiment, 15 N-labeled bacterial cells were shifted to 14 N medium, at what we can designate as generation 0. What proportion of 15 N- 15 N, 15 N- 14 N and 1 14 N- 14 N DNA would you expect to find at generations 1, 2 and 3? Generation 1: All of the DNA will be 15N/14N Generation 2: Half of the DNA would be 15N/14N and half will be 14N/14N Generation 3: ¼ of the DNA will be 15N/14N and ¾ of the DNA will be 14N/14N